The present invention relates to catheters, cannulae, and the like, and particularly to catheters that are steerable through body cavities and aimable at obstructions, organs, or tissue within the body from a position external to the body. More particularly, the present invention relates to a tube provided at the distal end of a catheter and apparatus that is operable to position or center the tube within a body cavity.
A great deal of research effort has focused on providing a catheter having a distal end which, when inserted into a body, is readily steerable and aimable to advance the catheter through body cavities and passageways. It has been observed that materials exhibiting mechanical memory properties triggered by heat are particularly useful for enhancing the maneuverability of catheters or like devices. The materials are commonly called "temperature-activated memory materials" or "shape memory alloys" because they move to assume a predetermined shape when heated to a predetermined temperature.
Nitinol, a nickel-titanium alloy, is one such temperature-activated memory material that has been formed into memory element strips and deployed in the distal end of a catheter. Heating the nitinol memory element strips to a given temperature using an electric current provided by a power supply causes the memory elements to deform to assume a predetermined shape, thereby deflecting the distal end of the catheter. See, for example, U.S. Pat. Nos. 4,543,090; 4,601,705; and 4,758,222 for descriptions of known memory element systems for steering and aiming catheters, cannulae, and the like.
While devices of the type described above enable an operator to steer a catheter by remote control to a particular destination within a body cavity, it is often necessary to position the catheter precisely in a certain location or orientation within the cavity once the destination is reached. For example, once a catheter has reached its destination, it might be desired to center the catheter within the cavity to aim a laser beam or the like emanating from the catheter precisely in a predetermined direction.
Alternatively, upon arrival of the catheter at its destination, certain applications might require the catheter to shift within the cavity to an off-center position close to an interior wall of the body cavity. Foreign matter, such as plaque, is known to accumulate on the interior walls of certain body cavities reachable by a steerable catheter. In such circumstances, foreign matter on the interior wall of a body cavity could be dislodged more easily using a catheter of enhanced maneuverability that could be shifted by remote control to an off-center position within the body cavity directly contacting the foreign matter.
One object of the present invention is to provide a readily steerable catheter, cannula, or the like which has a distal end that is easily maneuvered by remote control to occupy a predetermined position or orientation within a body cavity once the catheter has been steered through the body cavity to reach its destination.
Another object of the present invention is to provide an apparatus at the distal end of a catheter, cannula, or the like which is operable by remote control to move the distal end to a "centered" position along the central axis of the body cavity. In come cases, it also may be desirable to move the distal end to a predetermined off-center position within the body cavity.
Yet another object of the present invention is to provide a catheter, cannula, or the like having a distal end that includes scoop means for collecting plaque or other foreign matter accumulated on an interior wall of a body cavity and an apparatus that is operable by remote control to engage an interior wall of the body cavity and push the scoop means into a mound of plaque accumulated on another portion of the interior wall of the body cavity so that some of the plaque is deposited into a collection space formed in the catheter.
According to the present invention, an apparatus is provided for positioning a core member within a passageway formed in a body. The apparatus includes means for moving the core member relative to an internal wall defining the passageway. The moving means includes at least one temperature-activated memory element having spaced-apart attachment portions and a shape memory portion disposed therebetween. The spaced-apart attachment portions are coupled to the core member, while the shape memory portion is configured to move with respect to the core member when heated to a predetermined temperature.
The apparatus also includes control means for selectively heating the at least one memory element to the predetermined temperature. When so heated, the shape memory portion of the at least one memory element moves away from the core member to engage the internal wall of the passageway, thereby positioning the core member in a preselected orientation or position within the passageway. The control means is coupled to the attachment portions of the at least one memory element.
According to one aspect of the present invention, the apparatus includes several temperature-activated memory elements spaced equiangularly about the circumference of a tubular core member provided at the distal end of a catheter. When electrical current is supplied to heat the memory elements to a predetermined temperature, they expand outwardly away from the core member to engage the internal wall of the passageway containing the core member so as to center the core member along a central axis of the passageway. The core member will remain in its centered position as long as the memory elements are heated to their predetermined temperature.
According to another aspect of the present invention, the apparatus includes at least one temperature-activated memory element positioned on a tubular core member so that upon being heated to its predetermined transformation temperature, the memory element expands outwardly away from the core member to engage a particular portion of an interior wall of a passageway. The movement of the memory element away from the core member and against the wall portion moves the core member toward an opposite wall portion of the passageway. Thus, the core member is moved to a specified "off-center" position within the passageway.
In one embodiment, the tubular core member is formed to include a hollow interior cavity. Scraping means provided within the interior cavity is movable therein past a side opening formed in the core member. Advantageously, the core member can be moved by remote control using the inventive apparatus to the off-center position so that an accumulation of plaque or other foreign matter on an internal wall of the passageway is introduced into the hollow interior cavity through the side opening in the tubular core member. The scraping means is movable within the tubular core member to displace plaque admitted into hollow interior cavity and move it further into a collection space provided at one end of the cavity for storage. The catheter can then be removed from the patient and the plaque that was gathered and stored in the catheter can be removed from the catheter for analysis or disposal.
According to yet another aspect of the present invention, the apparatus includes a tubular core member having a heat-conductive tip affixed at its distal end and also includes means extending through tubular core member for conducting heat to the heat-conductive tip. For example, laser or fiber optics means could be employed to provide the heat-conducting means. The apparatus also includes at least one temperature-activated memory element having an end affixed to the heat-conductive tip. Advantageously, heat is conducted through the tubular core member to heat the heat-conductive tip. Heat from the tip is transferred to the temperature-activated memory element by conduction to heat the memory element to its transformation temperature. The temperature-activated memory element expands upon heating to engage an interior wall of a passageway to position the core member within the passageway.
According to still another aspect of the present invention, the apparatus includes at least one control element coupled to a tubular core member. In a preferred embodiment, the control element is a temperature-activated memory element. The control element has a flexible central portion lying between a pair of end portions. The apparatus also includes means for anchoring a first of the end portions to a proximal end of the core member. In addition, the apparatus includes collar means for slidably coupling a second of the end portions to a distal end of the core member. Advantageously, the flexible central portion can move away from the core member to engage an interior wall in a body passageway as the collar means attached to the second end portion slides on the distal end of the core member. This sliding movement can occur even though the first end portion is rigidly fixed to the proximal end of the core member.
According to yet another aspect of the present invention, the apparatus includes means for anchoring both first and second end portions of each of at least one control element to a core member. Again, each control element is desirably a temperature-activated memory element. A flexible central portion lying between the end portions of each control element is free to move relative to the core member to engage an interior wall in a body passageway without causing the end portions to move relative to the core member. Advantageously, the flexible central portion may be initially allowed to assume an undetermined configuration. It can then be moved (e.g. by heat in the case of a temperature-activated memory element) to assume a predetermined configuration acting against an interior wall in a body passageway to cause the core member to move to assume a predetermined location or orientation within the body passageway.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.